Sickle cell disease is the most common inherited blood disorder and it leads to significant morbidity and mortality. Adolescents with this disease are at a particularly high risk of death because they are frequently unprepared to manage their medications at the time of transition to adult care providers. Hydroxyurea is the only disease-modifying medication available for patients with sickle cell disease. While multiple clinical trial show that hydroxyurea can reduce complications, refill records indicate that few patients adhere to hydroxyurea at the levels achieved in clinical trials. Poorly adherent patients have worse health outcomes than those with high adherence. Despite this, adherence interventions remain untested. My long-term goal is to become an independent clinical investigator in sickle cell disease and medication adherence. The objective of my proposed study is to determine the impact of an innovative electronic tool, called Mobile Directly Observed Therapy, or Mobile DOT. Mobile DOT uses alert messages, videos, feedback, and incentives to encourage hydroxyurea adherence in children and adolescents with sickle cell disease. Specifically, this study aims to determine: (1) if Mobile DOT improves hydroxyurea adherence as measured by refill records (2) if hydroxyurea biomarkers, self-reported adherence, and refill adherence are valid hydroxyurea adherence measures, and (3) if Mobile DOT leads to improved self-management skills in adolescent participants. My career development plan includes mentorship, formal coursework, and seminars in three focus areas: behavioral theory, adolescent and young adult transition, and clinical trial and cost-effectiveness studies. Nationwide Children's Hospital provides an ideal setting for this research because it has a large population of children and adolescents with sickle cell disease and the strong institutional support to complete health services research projects. Results from this study will inform the design of the definitive multi-center study that will seek to determine if an electronic adherence tool for hydroxyurea is cost-effective and leads to improved outcomes for children and adolescents with sickle cell disease.